All I can find online are descriptions on how active buzzers have an oscillator built in so that you just need to feed them a DC and they buzz at the frequency set by such oscillator, but I haven't been able to find either a diagram, description or teardown of an active buzzer to see how is this usually done.
I can easily see how to build an active buzzer from a passive buzzer providing one of infinite possible ways of implementing an oscillator, but I wonder how is it actually done, specially on the tiny packages.
I've seen a teardown here, fantastic BTW, but I assume there are other much simpler/cheaper constructions.